Mixed-metal system conductors for use in low-temperature co-fired ceramic circuits and devices
A composition for forming transition vias and transition line conductors is disclosed for minimizing interface effects at electrical connections between dissimilar metal compositions. The composition has (a) inorganic components selected from the group consisting of (i) 20-45 wt % gold and 80-55 wt % silver and (ii) 100 wt % silver-gold solid solution alloys, and (b) an organic medium. The composition may also contain (c) 1-5 wt %, based upon the weight of the composition, of oxides or mixed oxides of metals selected from the group consisting of Cu, Co, Mg and Al and/or high viscosity glasses mainly containing refractory oxides. The composition may be used as a multi-layer composition in a via fill. Multi-layer circuits such as LTCC circuits and devices may also be formed using the composition for forming transition vias and transition line conductors.
1. A process to produce a composition for forming transition vias and transition line conductors comprising the steps of:
a. providing a first layer comprising inorganic components selected from the group consisting of 20-45 wt % gold and 80-55 wt % silver dispersed in organic medium;
b. providing a second layer comprising 100 wt % silver-gold solid solution alloys dispersed in organic medium;
c. applying the first layer to partially fill a via;
d. applying the second layer to the first layer to fill the via; and
e. co-firing the first layer and the second layer in the via,
wherein the first layer and the second layer are in electrical contact with each other, wherein the wt % of gold in the inorganic component of the first layer is greater than the wt % of gold in the inorganic component of the second layer, wherein the difference in diffusion coefficients of the first layer and the second layer is negligible.
2. The process of claim 1 further comprising providing 1-5 wt %, based upon the weight of the composition, of oxides or mixed oxides of metals selected from the group consisting of Cu, Co, Mg and Al and/or high viscosity glasses containing refractory oxides.
3. A composition produced by the process of claim 1 or 2 .
4. A circuit comprising the composition of claim 3 , the circuit having at least a first electrical connection and a second electrical connection, said first electrical connection being to a gold line conductor or a gold via and said second electrical connection to a silver line conductor or a silver via, wherein the transition line conductor contacts the first electrical connection at only one interface and the second electrical connection at only one interface, wherein interface of the first and second electrical connection are different, wherein the transition line conductor is not positioned perpendicular across a via.
5. A multi-layer transition via comprising the composition of claim 3 .